1. Field of the Invention
The present invention generally relates to semiconductor devices and methods for manufacturing the same. More particularly, the present invention is directed to a semiconductor device capable of improving mounting reliability and to a method for manufacturing the same.
2. Description of the Related Art
In recent years, high-density integration and miniaturization technology of semiconductor devices has been progressed, and electronic appliances tend to be more miniaturized, light-weighted, and have higher performance. Due to these facts, semiconductor devices are increasingly accelerated to have higher-density integration and higher functionality, such as the ASICs (Application-Specific Integrated Circuits) in LSI (Large Scale Integration). In such semiconductor devices with high-density integration and high functionality, the total number of external terminals (pins) and the layout of more terminals (pins) are being required to be increased.
Examples of such semiconductor devices are semiconductor packages that include IC chips, LSI chips, or other semiconductor chips mounted on a lead frame and sealed with dielectric-resin. As these semiconductor packages, types that are thin and have small mounting area such as QFN (Quad-Flat No-lead) packages and SON (Small Outline No-lead) packages are known. The resin-sealed types of semiconductor devices, called BGAs (Ball Grid Arrays), that are surface-mounted types of packages with solder balls serving as external terminals of the package, are also mass-produced. In addition, semiconductor devices called LGAs (Land Grid Arrays) are present as another surface-mounted type of packages. In LGAs, matrix-formed planar electrodes are provided as external terminals thereof instead of the solder balls provided in a BGA.
Examples of these conventional semiconductor devices are described in, for example, JP-A-8-227964 (1996) and JP-A-8-138988 (1996).
The semiconductor integrated circuit device disclosed in JP-A-8-227964 includes a lead frame with a circular outline and leads extending radially from a die pad disposed centrally. According to JP-A-8-227964, this conventional semiconductor-integrated circuit device has high mounting reliability for a gull-wing lead package. However, this conventional circuit device does not meet the needs of recent years for the thinning-down and downsizing of packages.
In addition, although JP-A-8-138988 describes a package including a chip of a polygonal shape with at least six sides (or of a circular shape), it is considered to be difficult to fabricate such a polygonal or circular chip.
Recently, compact semiconductor devices of lead frame types (QFN, SON, LGA, etc.), for example, are being required to have further improved mounting reliability. When a semiconductor is used in a high-temperature environment, for example in an automobile, thermal stresses are applied to the semiconductor device. Mounting reliability against such thermal stresses is particularly expected to be further improved by bringing a thermal expansion coefficient of the semiconductor device close to that of its mounting substrate.
Meanwhile, the semiconductor package of a BGA type semiconductor device disclosed in JP-A-2001-230338 has an insulating substrate formed in a circular shape so that the stresses do not concentrate at corners, and instead be applied equally according to the distance from the center. This BGA type of semiconductor device is enhanced in reliability against thermal shocks and other environmental changes. However, when mounting reliability against thermal stresses is to be further improved, such construction may be insufficient.